Constant lead edge paper inverter system

ABSTRACT

A printing apparatus capable of duplex imaging that maintains the lead edge of a sheet constant, is disclosed. The printing apparatus includes a first transport path to route a sheet along a processing direction, an edge position detector to detect a lead edge of the sheet, a marking device that prints on a first side of the sheet, a second transport path to receive the sheet from the marking device, and an inverter mechanism that receives the sheet from the second transport path and inverts the sheet along a cross-processing direction that is perpendicular to the processing direction. The printing apparatus also includes a third transport path that receives the inverted sheet and routes the inverted sheet back to the first transport path. With this configuration, upon being routed back to the first transport path, the edge position detector detects the same lead edge of the sheet as previously detected and the marking device prints on a second side of the sheet.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present disclosure relates to digital document production equipment and, more specifically, to duplex capable imaging machines.

2. Description of Related Art

Digital document production equipment is very common in today's office environment. Generally, such equipment, which includes printers, copiers, facsimiles, or other multifunction machines, is configured to place text and images, based on digital data, onto media, such as paper sheets.

By way of example, consider the case of digital copiers, where original documents bearing images to be recorded on paper sheets are typically loaded into the tray of a document handler. The documents are drawn one sheet at a time and moved relative to an image sensor. The image sensor records reflected light from a series of small areas in the original image as the image moves past the sensor to yield a set of digital signals representative of the image to be recorded on a sheet of paper. The digital signals are then supplied to a marking device, such as, for example, an electrophotographic laser printing device or an inkjet printhead device, which renders the recorded image on one side of the sheet of paper as the sheet passes across the marking device.

To ensure proper image placement and alignment, the digital copier also employs an edge position detector. The edge position detector is configured to determine the location of a side edge of the sheet relative to a fixed point within the copier. That is, prior to subjecting the sheet to the marking device, the sheet passes over the edge position detector that registers the side edge of the sheet to ensure proper alignment and placement of the recorded image as the sheet is guided across the marking device.

More sophisticated types of document production equipment are also capable of rendering images on both sides of a single sheet of paper, a feature commonly referred to as “duplexing” or “duplex imaging.” In order to print on both sides of the same sheet, duplex capable machines typically feed a sheet through the edge detector and marking device a first time to receive a first image on one side thereof, suck the sheet back out, invert or flip the sheet, and then re-feed the sheet back through the edge detector and marking device so that the device can place a second image on the opposite side of the sheet. The path by which the sheet has been output by the marking device, inverted, and re-fed back to the marking device, is generally referred to as the “duplex path.” Although the specific architectures vary, most conventional duplex paths employ an inverter transport loop that guides the lead edge of the paper sheet over the trail edge to effectively flip the sheet.

Ideally, the registration of duplexed images should result in images recorded on opposite sides of the sheet to be substantially aligned with each other. In other words, the margins of the images on opposite sides of the sheet should appear to be superimposed. However, as a practical matter, after the sheet has been sucked out and flipped by the inverter transport loop, the edge detector registers the side edge of the sheet that is opposite to the initially detected side edge, in anticipation of the sheet being re-fed back to the marking device. It will be appreciated that, given paper length and cut angle tolerances, the use and registration of opposite side edges increases the risks of duplex image misalignment and placement errors.

SUMMARY OF THE INVENTION

Principles of the present invention, as embodied and broadly described herein, provide a printing apparatus capable of duplex imaging that maintains the lead edge of a sheet constant. In one embodiment, the printing apparatus includes a first transport path to route a sheet along a processing direction, an edge position detector to detect a lead edge of the sheet, a marking device that prints on a first side of the sheet, a second transport path to receive the sheet from the marking device, and an inverter mechanism that receives the sheet from the second transport path and inverts the sheet along a cross-processing direction that is perpendicular to the processing direction. The printing apparatus also includes a third transport path that receives the inverted sheet and routes the inverted sheet back to the first transport path. With this configuration, upon being routed back to the first transport path, the edge position detector detects the same lead edge of the sheet as previously detected and the marking device prints on a second side of the sheet.

Other embodiments include a method of printing on opposite sides of a sheet, comprising routing the sheet across a first transport path along a processing direction, detecting a lead edge of the sheet, printing on one side of the sheet, routing the sheet across a second transport path, inverting the sheet along a cross-processing direction that is perpendicular to the processing direction, and routing the sheet across a third transport path that feeds back towards the first transport path. The method further includes detecting the same lead edge, and printing on a second side of the sheet.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the present patent specification, depict corresponding embodiments of the invention, by way of example only, and it should be appreciated that corresponding reference symbols indicate corresponding parts. In the drawings:

FIG. 1 depicts the principle of elements of duplex-capable printing apparatus, in accordance with an embodiment of the present invention;

FIG. 2A depicts features of a sheet to be processed by the duplex-capable printing apparatus of FIG. 1; and

FIG. 2B is a simplified diagram of FIG. 1 that depicts the orientation and alignment of a sheet at different time intervals.

DETAILED DESCRIPTION OF THE INVENTION

As will be evident by the ensuing detailed description, the present invention provides a printing apparatus and method of providing duplex imaging with single lead edge registration.

FIG. 1 schematically depicts the principle elements of the image processing station of a duplex capable printing apparatus 100, in accordance with an embodiment of the present invention. Such an apparatus is intended to cover printers, copiers, facsimiles, or other multifunction machines that are capable of duplex imaging. As illustrated in FIG. 1, printing apparatus 100 comprises a side edge position detector 110, a marking device 120, a simplex transport path 130, and a constant lead edge paper inverter system 160. In turn, constant lead edge inverter system 160 comprises an upper duplex transport path 140 and a lower duplex transport path 150. The orientation of FIG. 1 is depicted so that the image processing direction, that is, the general direction in which a sheet of paper is transported and routed to receive an image, is indicated by P, while the cross processing direction (i.e., perpendicular to P) is indicated by P′.

As shown in FIG. 1, simplex transport path 130, configured for single-sided imaging and for accommodating possible duplex imaging, comprises a plurality of drive roller nips 102 oriented to guide a sheet of paper across side edge position detector 110 and marking device 120 along the image processing direction P. That is, in the case of single-sided imaging in which the digital signals representative of the captured image have been supplied to marking device 120, the sheet is supplied to and enters the simplex transport path 130 at intake portion 131 and drive roller nips 102 engage the sheet and transport the sheet across side edge position detector 110. Side edge position detector 110 registers the side edge of the sheet, in this case, the lead edge, to ensure proper alignment and placement of the recorded image. After registering the side edge, drive roller nips 102 guide the sheet across marking device 120 to record the captured image onto one side of the sheet. Finally, the single-sided imaged sheet is then routed to an output portion 139 of simplex path 130.

As noted above, constant lead edge inverter system 160 comprises an upper duplex transport path 140 and a lower duplex transport path 150. In turn, upper duplex transport path 140 comprises U-shaped inverter 145, a plurality of drive roller nips 102 configured to guide and transport the sheet to inverter 145, a plurality of cross-direction drive roller nips 142 and a sensor 143 configured to identify the lead edge of the sheet at a constant stop point S. U-shaped inverter 145 may comprise rolls, vacuum transport, or any mechanism suitable for such purposes.

Both U-shaped inverter 145 and cross-direction drive roller nips 142 are oriented and configured to operate along the cross-process direction P′ direction. In particular, the combination of U-shaped inverter 145 and cross-direction drive roller nips 142 cooperate to receive and engage the sheet of paper containing a previously recorded image on one side, flip the sheet along the cross-process direction P′ to the opposite side, and forward the flipped sheet to lower duplex transport path 150.

Lower duplex transport path 150 is configured to receive and route the flipped sheet back over to the intake portion 131 of simplex transport path 130 in order for the marking device 120 to record a second image on the blank side of the sheet.

In an exemplary embodiment, consider the case in which duplex imaging has been selected and the two images to be recorded on opposite sides of the sheet have been digitally captured by the image sensor (not shown), so that the digital signals representative of the captured images have been supplied to marking device 120. Initially, much like the single-sided imaging case, the sheet is supplied to and enters the simplex transport path 130 at intake portion 131, so that drive roller nips 102 engage the sheet and transport the sheet across side edge position detector 110. The detector 110 registers the side edge (i.e., the lead edge) of the sheet to ensure proper alignment and placement of the first recorded image. After registering the side edge, drive roller nips 102 guide the sheet across marking device 120 to record the first captured image onto one side of the sheet. However, unlike the single-sided imaging case, where the single-sided imaged sheet is routed the to output portion 139, the sheet is routed to duplex path intake portion 141.

For the sake of clarity regarding the subsequent description of constant lead edge inverter system 160, reference is made to FIGS. 2A, 2B. FIG. 2A illustrates a sheet having a blank side SH1 onto which a second image will be recorded thereon, a side SH2 having a first recorded image, and the lead side edge E of the sheet having been identified and registered by side edge position detector 110. FIG. 2B illustrates the operation of constant lead edge inverter system 160 at different time intervals ti.

With this said, time interval t1 represents the sheet after passing through side edge position detector 110 and marking device 120, in which the first image is recorded on side SH2. After time interval t1, the sheet is routed to duplex path intake portion 141 where the drive roller nips 102 engage the sheet and transport the sheet along the upper process direction P, as indicated by time interval t2.

The sheet continues to be transported along the upper process direction P until reaching the upper drive roller nips 102 at the U-shaped inverter 145, as indicated by time interval t3. At this point, sensor 143, disposed proximate to the distal end of U-shaped inverter 145, identifies the lead edge of the sheet at a constant stop point S under the cross-direction drive roller nips 142. Upon reaching constant stop point S, the sheet is stopped and cross-direction drive roller nips 142 engage the sheet while drive roller nips 102 disengage. As depicted in FIG. 2B, the sheet is turned upside down so that recorded side SH2 is on top and blank side SH1 is on the bottom. It will be appreciated that, at this point, other quality control measures may be taken to further ensure proper alignment and image placement. For example, with the sheet being in a prone position on top of U-shaped inverter 145, gross deskewing and top edge registration could be performed to measure and account for side edge skew.

At time interval t4, the cross-direction drive roller nips 142 drive the sheet in the cross-process direction P′ of the U-shaped inverter 145. The combination of cross-direction drive roller nips 142 and inverter 145 effectively flips the sheet and feeds the sheet to lower duplex transport path 150, where the cross-direction drive roller nips 142 disengage and drive roller nips 102 on the lower path engage the sheet. As depicted in FIG. 2B, the flipping results in the sheet having blank side SH1 on top while recorded side SH2 is on the bottom. However, as also indicated in the figure, the lead edge E remains on the same side after the sheet is flipped.

As indicated by time interval t5, the lower path drive roller nips 102 transport the sheet along the lower processing path onto duplex output portion 159, which directs the sheet back into a beginning portion of simplex path 130.

At time interval t6, the sheet is placed back on simplex path 130 prior to being imaged for the second time. As depicted in FIG. 2B, by virtue of the lower duplex transport path 150, the sheet is once again turned upside down so that recorded side SH2 is on top and blank side SH1 is on the bottom. However, as noted above, lead edge E of the sheet remains on the side after the sheet is flipped. Subsequently, the drive roller nips 102 on the simplex path 130 engage the sheet and transport the sheet across side edge position detector 110, detector 110 registers the same lead edge E of the sheet, as previously registered. After registering the lead edge E, drive roller nips 102 guide the sheet again across marking device 120 to record the second captured image onto the blank side SH1 of the sheet, and thereafter, the duplex imaged sheet is routed to output portion 139.

Given the above-described configuration, printing apparatus 100 is capable of rendering images on both sides of the sheet while maintaining the same lead edge. The presentation of the same lead edge to the edge detector for both the pre-inverted and post-inverted sheet, reduces the risks of duplex image misalignment and placement errors due to the use and registration of opposite side edges. Other advantages may include higher throughput speeds, as the cross-direction drive roller nips do not have to reverse directions as conventional roller nips do when the sheets have to be sucked back out prior to flipping.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

1. A printing apparatus, comprising: a first transport path configured to route a sheet along a processing direction; an edge position detector configured to detect a lead edge of the sheet; a marking device configured to print on a first side of the sheet; a second transport path configured to receive the sheet from the marking device; an inverter mechanism configured to receive the sheet from the second transport path and invert the sheet along a cross-processing direction that is perpendicular to the processing direction; and a third transport path configured to receive the inverted sheet and route the inverted sheet back to the first transport path, wherein, upon being routed back to the first transport path, the edge position detector detects the same lead edge of the sheet and the marking device prints on a second side of the sheet.
 2. The printing apparatus of claim 1, wherein the inverter mechanism comprises a U-shaped inverter.
 3. The printing apparatus of claim 2, wherein the U-shaped inverter includes a plurality of rolls.
 4. The printing apparatus of claim 2, wherein the U-shaped inverter includes a vacuum transport.
 5. The printing apparatus of claim 1, wherein the first, second, and third transport paths are arranged to form a circuit path.
 6. The printing apparatus of claim 1, wherein the first, second, and third transport paths include a plurality of drive roller nips that engage the sheet and are oriented and aligned to guide the sheet along the processing direction.
 7. The printing apparatus of claim 1, wherein the inverter mechanism includes a plurality of cross-drive roller nips that engage the sheet and are oriented and aligned to guide the sheet along the cross-processing direction.
 8. The printing apparatus of claim 1, wherein the first transport path includes an input portion to initially receive the sheet and an output portion to output the sheet.
 9. The printing apparatus of claim 1, wherein the second transport path includes an intake portion to receive the sheet from the first transport path.
 10. The printing apparatus of claim 1, wherein the third transport path includes an output portion to direct the sheet back to the first transport path.
 11. A sheet inverter mechanism, comprising: a U-shaped inverter configured to receive a sheet along a processing direction; and a plurality of roller nips oriented and arranged to engage and drive the sheet across the U-shaped inverter to invert the sheet, the sheet being inverted along a cross-processing direction that is perpendicular to the processing direction, wherein a lead edge of the sheet prior to being inverted remains on a same side after being inverted.
 12. A method of printing on opposite sides of a sheet, comprising: routing the sheet across a first transport path along a processing direction; detecting a lead edge of the sheet; printing on one side of the sheet; routing the sheet across a second transport path; inverting the sheet along a cross-processing direction that is perpendicular to the processing direction; routing the sheet across a third transport path that feeds back towards the first transport path; detecting the same lead edge; and printing on a second side of the sheet.
 13. The method of claim 12, wherein the inverting of the sheet includes engaging and driving the sheet across a U-shaped inverter along the cross-processing direction.
 14. The method of claim 12, wherein the first, second, and third transport paths are arranged to form a circuit path.
 15. The method of claim 12, wherein the routing of the sheet within the first, second, and third transport paths includes the use of a plurality of drive roller nips that are oriented and aligned to engage and guide the sheet along the processing direction.
 16. The method of claim 12, wherein the inverting of the sheet includes the use of a plurality of cross-drive roller nips that are oriented and aligned to engage and guide the sheet along the cross-processing direction. 